March 13, 2019: Long lines. Narrow seats. Baggage fees. You recognize this list. It’s the downside of flying on modern commercial airlines. And now we have a new item to add: cosmic ray neutrons.

Spaceweather.com and Earth to Sky Calculus have just completed a 5-continent survey of neutron radiation at aviation altitudes. From December 2018 through February 2019, Hervey Allen of the University of Oregon’s Network Startup Resource Center carried Earth to Sky radiation sensors–including neutron bubble chambers–onboard commercial flights from North America to Europe, Africa, South America and Asia.

Hervey logged 83 hours in the air as he traveled 41,500 miles above 30,000 feet. For reference, that’s almost twice the circumference of the Earth. The entire time, he gathered data on X-rays, gamma-rays and neutrons in an energy range (10 keV to 20 MeV) similar to that of medical radiology devices and “killer electrons” from the Van Allen Radiation Belts.

The results were eye-opening. During the trip, Hervey recorded 230 uGy (microGrays) of cosmic radiation. That’s about the same as 23 panoramic dental x-rays or two and a half chest X-rays. Moreover, 41% of the dose came in the form of neutrons. This confirms that cosmic-ray neutrons are abundant at aviation altitudes and must be considered in any discussion of “Rads on a Plane.”

Researchers have long known that cosmic rays penetrate airplanes. Our own 3-year survey of global radiation shows that X-rays and gamma-rays at aviation altitudes are typically 50 times stronger than sea level. This new survey focuses on neutrons, a more potent type of radiation from deep space. Studies show that neutrons can be ten times more effective at causing biological damage compared to X-rays and gamma-rays in the same energy range. Neutrons are so effective, they are used for cancer therapy, killing tumors better than other forms of radiation.

Should we be worried about Hervey? Although he absorbed a lot of radiation during the survey, he did so slowly. Hervey’s whole body dose was spread out over 14 flights and 3 months–unlike, say, a dental X-ray which is localized to the jaw and delivered in a split-second. Slow delivery gives the body time to respond, repair damage, and move on without obvious health effects. On the other hand, at least one study shows that low-dose radiation received over a long period of time may slightly increase the risk of leukaemia, while flight attendants have been found to have a higher risk of cancer than the general population.

Our survey also revealed some geographical variations. Generally speaking, neutron radiation was stronger near the Arctic Circle and weaker near the equator. It was weakest of all, however, in flights over Chile as the aircraft skirted the South Atlantic Anomaly. We will be investigating these variations with additional flights in the near future.

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3 thoughts on “Neutrons Detected on Commercial Airplane Flights”

GabrielMarch 13, 2019 / 9:55 am

Chile is not considered to be inside the region of the South Atlantic Anomaly but right in the border. Measurements on Earth’s mahnetic field out there are much higher than those in the north of Argentina and south of Brazil. And the SAA centre seems to be moving north at the moment.

Abstract
The South Atlantic Anomaly (SAA) is a region of reduced magnetic intensity where the inner radiation belt makes its closest approach to the Earth’s surface. Satellites in low-Earth orbit pass though the SAA periodically, exposing them to several minutes of strong radiation each time, creating problems for scientific instruments, human safety, and single event upsets (SEU). For the first time, we are able track the SAA movement continuously over 27 years, using overlapping satellites in similar orbits with similar instruments. The Defense Meteorological Satellite Program(DMSP) spacecraft have been carrying the Special Sensor J (SSJ) precipitating energetic particle spectrometers since 1982. The instruments are susceptible to MeV electrons and protons that pass through the spacecraft skin and instrument case and get counted. This “backgroundˮ is easily identified and we use it to map the movement of the SAA. Comparison with energetic particle data from the Energetic Particle Telescope (EPT) instrument on the Proba-V spacecraft indicates that the best match with the SSJ data occurs in the energy range above about 2.6 MeV for electrons and above about 29 MeV for protons. The peak flux and extent of the SAA from both the SSJ and EPT instruments are nearly identical in longitude while in latitude, the peak EPT flux is 5° south of the peak SSJ flux. However, the shapes of the SAA in latitude and the locations of the outer radiation belts are nearly identical. We find that the SAA moves 0.06° N/yr and 0.28° W/yr. We also find a difference with the movement and location of the SAA from the contamination by high energy particles on the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) instrument on DMSP F16 (Shaefer et al., 2016). However, the SSUSI instrument is located on the opposite side/bottom of the spacecraft and Shaefer et al. (2016) estimated that most of the particle noise pulses in the SSUSI instrument are produced by protons greater than about 45 MeV. Thus the contamination in the SSUSI instrument is produced by a different population of particles that the contamination in the SSJ/5 instrument which would lead to differences in movement and location of the SAA. While this study focuses on the SAA movement on a yearly basis, further analysis will allow us to investigate the movement on shorter time scales, the variation of the flux intensity, the spatial extent of the SAA, and the dynamics of the outer radiation belt.

“On the other hand, at least one study shows that low-dose radiation received over a long period of time may slightly increase the risk of leukaemia, while flight attendants have been found to have a higher risk of cancer than the general population.”

Sorry but a study that cannot fully account for sleep disruption and the effect on general health does not seem to be of much value, particularly when accurate data on all variables that matter is hard to gather.